Thomas Stevenson | |
|---|---|
 Stevenson in 1880 | |
| Born | (1818-07-22)22 July 1818 Edinburgh, Scotland |
| Died | 8 May 1887(1887-05-08) (aged 68) Edinburgh, Scotland |
| Occupation | Lighthouse engineer |
| Employer | Northern Lighthouse Board |
| Spouse | |
| Children | Robert Louis Stevenson |
| Parent(s) | Robert Stevenson (father) Jean Smith (mother) |
| Relatives | David Stevenson (brother) Alan Stevenson (brother) |
| Signature | |
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Thomas StevensonPRSEMInstCEFRSSAFSAScot (22 July 1818 – 8 May 1887) was a pioneering Scottishcivil engineer,lighthouse designer andmeteorologist, who designed over thirty lighthouses in and around Scotland, as well as theStevenson screen used in meteorology. His designs, celebrated as ground breaking, ushered in a new era of lighthouse creation.
He served as president of theRoyal Scottish Society of Arts (1859–60), as president of theRoyal Society of Edinburgh (1884–86), and was a co-founder of theScottish Meteorological Society.[1]
He was the father of writerRobert Louis Stevenson.
He was born at 2 Baxters Place[2] inEdinburgh, on 22 July 1818, the youngest son of engineerRobert Stevenson, and his wife (and step-sister) Jean Smith. He was educated at the Royal High School in Edinburgh.
Thomas Stevenson was a devout and regular attendee at St. Stephen's Church inStockbridge, at the north end of St Vincent Street, Edinburgh.
He lived with his family at Baxters Place until he got married in 1848. He then got a house at 8 Howard Place.[3] By 1855 he moved to 1 Inverleith Terrace.[4] From at least 1860 he lived at 17Heriot Row, a large Georgian terraced townhouse inEdinburgh's New Town.[5]
In 1864, he publishedThe design and construction of harbours: a treatise on maritime engineering. The book was based on an article he had originally written for theEncyclopædia Britannica, and covered the principles and practices involved inharbour design and construction. The work discussed thegeological and physical features affecting harbour design, the generation and impact ofwaves, along with construction materials andmasonry types forquay walls. The book also explored the efficacy oftides andfresh water in maintainingoutfalls. A second edition of the book was published in 1874.[6]
In 1869, as a successful experiment into using the newly inventedelectric light forlighthouses, Stevenson had an underwater cable installed from the eastern part ofGranton Harbour, and a light on the end of theTrinity Chain Pier was controlled from half a mile away by an operator on the harbour.[7][8] He designed theStevenson screen as a shelter to shieldmeteorological instruments, and this has been widely adopted.
He died at 17 Heriot Row inEdinburgh on 8 May 1887 and is buried in the Stevenson family vault inNew Calton Cemetery. The vault lies midway along the eastern wall.
In the course of his work as a lighthouse and harbour engineer, Stevenson had made observations ofwave heights at various locations in Scotland over a number of years. In 1852, he published a paper in which he suggested that waves increased in height by a ratio approximate to thesquare root of their distance from thewindward shore.[9] Stevenson developed this into the simple formula, in which is the wave height infeet and is thefetch inmiles.[10][11]
Essential components for wave height prediction, most notablywind speed, are missing from Stevenson's formula. In 1852, mathematical analysis of the theory of water waves, and methods for numerical assessment of factors such asshoaling andsurge, were in their infancy.[12][13] Stevenson's analysis[14] is possibly the first quantitative discussion of wave height as a (square root) function of fetch, and his paper[15] is one of the first quantitative studies of wind speeds in theplanetary boundary layer.
Modern analysis of Stevenson's formula indicates that it appears to conservatively estimate wave heights for wind speeds up to around 30miles per hour, being based on his observations which most likely were taken for fetch lengths under 100kilometres, withoutfully developed seas. The breakwater at Wick was exposed to a fetch length of approximately 500 kilometres, and wind speeds far in excess of 30 miles per hour, prior to its eventual destruction.[10][16]
In 1965, the South African engineerBasil Wrigley Wilson proposed a method which can be used to approximate the significant wave heightH1/3 and periodT1/3 of wind waves generated by a constant wind of speedU blowing over a fetch lengthF.[17] The units for these quantities are as follows:
Wilson's formulae apply when the duration of the wind blowing is sufficiently long, as when the wind blows for only a limited time, waves cannot attain the full height and period corresponding to the wind speed and fetch length.[18] Under conditions were the wind blows for a sufficiently long time, for example during a prolonged storm, the wave height and period can be calculated as follows:
In these formulae,g denotes the acceleration due to gravity, which is approximately 9.807 m/s2. The wind speedU is measured at an elevation of 10 metres above the sea surface. For conditions approximate to those for the Wick breakwater during a storm (fetch length of 500km, wind speed of around 75mph), the graph below shows that Wilson's method predicts a significant wave height (H1/3) of around 1.5 times that of Stevenson's.[9][17]
Nonetheless, whilst Stevenson's formula is highly limited and unsuitable for engineering design application, it was notable for being an early attempt to apply mathematical theory to hydraulic engineering problems, and shows some limited agreement (albeit within a narrow range) with a more advanced formula developed byRamón Iribarren in 1942.[16][19] A major flaw in Stevenson's formula is the absence of consideration of wind speed, and comparison with Wilson's formula at 3 different wind speeds (30, 50 and 75mph) shows only a reasonable level of agreement for 50mph winds at fetch lengths up to around 100 metres.[9][17]
Stevenson himself noted that the formula was anapproximation,[20] and actively encouraged further research into similar problems, imploring young engineers to redouble efforts in the advancement ofcoastal engineering during an 1885 address to the Institution of Civil Engineers in London.[21] In addition to his work on wave growth, he also undertook research into the phenomenon of wave decay insideharbour basins.[22]
Stevenson designed and supervised the construction of abreakwater atWick in 1863, which at the time was the largestherringfishery in Europe. The inner harbour, designed byThomas Telford, was completed in 1811, followed by the construction of the expanded outer harbour byJames Bremner between 1825 and 1834. However, by 1857, the need for increased capacity became evident, leading the British Fishery Society to propose a new breakwater. In 1862 Stevenson, along with his brother David, prepared detailed plans, sections, and specifications for the harbour's extension. This design received support fromSir John Coode andJohn Hawkshaw. A loan of £62,000 was sanctioned by A. M. Rendel, the engineer for thePublic Works Loan Commission.[23]
Construction commenced in April 1863, aiming for a final length of 460 metres. Stevenson's design featured a rubble mound extending to 5.5 metres above thelow water mark, following the Crane Rocks. This was capped with block walls and in-filled with rubble, providing asuperstructure up to 16 metres wide. The rubble for the mound was sourced from local quarries and transported bysteam locomotives. This was then deposited onto the breakwater mound using travellinggantries that ran along thestaging, marking a possible first in Scotland for this technique.[24][23] The seaward wall was constructed with a 6:1 batter. Below the waterline, the blocks were dry-jointed, whereas above the high-water mark, initiallyRoman and laterPortland cement mortar was used.[25]
The breakwater failed progressively as a result of severalstorms, and by 1870 it had lost one third of its length. It was eventually abandoned in 1877, after further severe storm damage, despite repeated failed attempts at its reconstruction.[16][23][25] Stevenson noted, in correspondence with theInstitution of Civil Engineers, that a single storm had at one stage removed 1,350tonnes of material from the breakwater, but he was unable to provide the height of the waves during the event.[26]
Applying present-day techniques to calculate local wave conditions demonstrates that the breakwater as built would not have survived without mobilising additional restraint, or a mechanism to abate wave forces.[25] Stevenson's own wave formula would have predicted offshore wave heights for Wick of around 8 to 10metres, whereas modern observations show that theNorth Sea exhibits wave heights of up to two to three times this figure.[27][28][29][10]
He was brother of the lighthouse engineersAlan andDavid Stevenson, between 1854 and 1886 he designed many lighthouses, with his brother David, and then with David's sonDavid Alan Stevenson.
He married Margaret Isabella "Maggie" Balfour in 1848, daughter of Rev Lewis Balfour. Their son was the writerRobert Louis Stevenson, who initially caused him much disappointment by failing to follow the engineering interests of his family.
His wife's younger brother,James Melville Balfour (i.e. his brother-in-law), trained under D. & T. Stevenson and then emigrated to New Zealand, where he was first the marine engineer forOtago Province before he was appointed Colonial Marine Engineer.[30][31]
